Safety isolation is an important consideration in the design of any electrical product that can expose users to potentially hazardous voltage levels. Manufacturers of such products need to ensure that their products are designed to adequately safe-guard against electrical shock.
In any safety isolation scheme, there is a certain amount of insulation required to create a protective isolation barrier between primary and secondary circuits. A primary circuit is a circuit that is directly connected to a line voltage and therefore has the potential to reach hazardous voltage levels. A secondary circuit is not electrically connected to the primary circuit (that is, there is no conductive connection between the secondary circuit and primary circuit) but could experience hazardous voltage levels if the insulation fails.
Underwriters Laboratories Inc. (UL) has developed a safety standard called UL 60950-1 (second edition), which specifies a high level of safety isolation to protect against risk of injury due to electric shock. The UL 60950-1 standard is based on the International Electrotechnical Commission (IEC) standard, IEC 60950-1 (second edition). The UL 60950-1 standard defines five categories of insulation: functional insulation; basic insulation; supplemental insulation; double insulation; and reinforced insulation. Functional insulation does not protect against electrical shock. Basic insulation is a single level of insulation that provides basic protection against electric shock. Supplemental insulation is independent insulation that can be applied in addition to basic insulation to reduce the risk of electrical shock in the event of a failure of the basic insulation. Double insulation comprises both basic insulation and supplemental insulation. Thus, basic insulation provides a single layer of insulating barrier between primary and secondary circuits, whereas double insulation provides two layers of insulating barrier between primary and secondary circuits. Reinforced insulation is a single insulation system that provides electrical shock protection equivalent to double insulation.
If a secondary circuit is not user-accessible, a basic level of isolation protection, that is, basic insulation, may be acceptable. Safety needs for products that include user accessible secondary circuits, on the other hand, demand two levels of protection provided by double insulation or its equivalent in reinforced insulation.
Integrated current sensors are known in the art. Illustrative current sensors of this type are sold under part numbers ACS712 and ACS722 by Allegro MicroSystems, LLC of Manchester, N.H., the Assignee of the subject application. These types of current sensors use a magnetic field transducer in proximity to a current conductor. The magnetic field transducer generates a signal having a magnitude proportional to the magnetic field induced by a current that flows through the current conductor.
Some current sensors may have the ability to provide reinforced isolation, or double isolation, as described in U.S. Pat. No. 8,907,437 entitled “Reinforced Isolation For Current Sensor With Magnetic Field Transducer” which Patent issued on Dec. 9, 2014 and which is assigned to the Assignee of the present application, the contents and teachings of which are hereby incorporated by reference in their entirety.